The IAPP Mission Statement and Core Programme specifies three principal axes of research for polynyas studies conducted under its aegis: 1) the generation of the polynya; 2) the ecosystem of the polynya; and 3) the role of the polynya in the carbon dioxide flux. As the IAPP programme progresses, these research axes are refined to incorporate knowledge acquired about polynya processes. The main scientific issues addressed by the NOW project are

(1) the oceanographic and meteorological processes that open and maintain the North Water;

(2) the hydrodynamic control of carbon cycling and primary production;

(3) the role of the North Water in sequestering atmospheric carbon dioxide;

(4) the potential impact of increased UV radiation on the biological productivity of the North Water;

(5) the role of biogenic DMS, a cloud nucleator, in determining local climate; 

(6) the distribution of air-borne contaminants in the trophic web;

(7) models of ice distribution in northern Baffin Bay;

(8) inverse models of the carbon flows in and outside the North Water;

(9) models of the potential impact of climate change on the dynamics of the North Water.

Assuming that the response of the North Water to global warming would be analogous to that of other Arctic waters, modeling efforts will provide unique insights into the potential fate of the entire marine Arctic ecosystem in the near future

General hypothesis for the North Water Polynya Project

The general hypothesis underlying much of the proposed research is that the very same physical processes that open the North Water are responsible for its unusual productivity. We hypothesize that both sensible and latent heat mechanisms contribute to the opening of the polynya, either simultaneously or separately at different times and in different areas of the North Water. Where and when sensible heat prevails, the stratification of the surface layer resulting from the melting of the ice cover will trigger an algal bloom immediately after the opening of the waters. By reducing vertical mixing, haline stratification also favors the warming of the surface layer. Where and when latent heat prevails, the algal bloom is delayed until solar heating stratifies the surface layer. The season of plankton production (the period between the algal bloom and the freeze up of the sea in the autumn) could last up to six months in the sensible heat case, four months in the latent heat case and two months at similar latitudes outside the North Water.

This lengthening of the production season and a warmer surface layer, in particular in the sensible heat case, would allow key metazoan species such as copepods, appendicularians and Arctic cod to accelerate growth and telescope their ontogenic development in the open waters of the polynya. According to our hypothesis, the early and sustained availability of plankton would explain the remarkable abundance of mammals and birds in the North Water.

Built around the central hypothesis, the science programme for NOW comprises three modules that each integrate several sub-projects: (1) physical generation of the North Water; (2) the North Water pelagic ecosystem; (3) biogeochemical cycling in the North Water. How the different sub-projects of the three modules are related to the central hypothesis and to each other and which countries participate in each sub-project is presented in the information Flow Chart of the NOW science plan. A synopsis of each sub-project with the Principal Investigators in charge is linked to the list below. You are welcome to contact project leaders for further information or details on specific research projects

Physical generation of the North Water polynya
Ocean Circulation and Hydrography
Ice Cover Dynamics 
Ice Physics
Modeling the Polynya and the Local Climate

The North Water pelagic ecosystem
Optics and Nutrients, Primary and Export Production 
Microbial-Metazoan Trophic Coupling
Plankton-Vertebrates Trophic Coupling
Carbon Flow, Contaminants and Trophic Structure
Impact of UV-B on Biological Productivity
Modeling Trophic Pathways
 

Biogeochemical cycling in the North Water
Carbon Cycling: Ecosystem Approach
Carbon Cycling: Direct Measurement Approach   
Microbial Particle Hydrolysis Below the Euphotic Zone
Cycling of Biogenic Sulfur Compounds

Physical generation of the North Water polynya

Ocean Circulation and Hydrography ( Ingram, leader )
Carmack, Galbraith, Gratton, Ingram, Marsden, Top.

The reduction of the ice cover that characterizes polynyas can occur in two ways: wind may remove the ice from an area faster than it is produced (latent-heat case) or warm waters may supply the heat necessary to melt the ice cover locally (sensible heat case). The two mechanisms are not exclusive and can contribute simultaneously to the opening of the polynya. Alternatively, each can prevail at a given period or in a given area of the polynya.

The North Water has been generally considered to result from an ice bridge that forms in narrow Smith Sound to the north of the polynya and blocks the southward flux of ice from the Arctic. However, remote sensing studies have found cells of warm water along the Greenland coast in winter. This influx of warm water may contribute to melt the ice cover and open the polynya along the Greenland coast. To understand the basic mechanisms responsible for the North Water, field measurements of the ocean circulation and temperature-salinity fields in the polynya and adjacent waters, especially off the west coast of Greenland, are needed. According to our general hypothesis, the mechanism of opening of the North Water also determines its biological productivity. It is thus imperative that the distribution in time and space of both sensible and latent heat processes be assessed with as much precision as possible.

Instruments that record the temperature, salinity and circulation will be moored in the polynya over at least two years. These data will be complemented by intensive shipboard sampling campaigns in late summer of 1997 (completed), spring and summer of 1998 and late summer of 1999. Merging the observational data with existing computer models will allow us to understand better why and how the North Water is formed.

Remote sensing of sea ice distribution, concentration, movement and type is central to the understanding of the generation of the North Water, as well as to the study of biological processes taking place in an outside the polynya. We will monitor the large-scale spatial and seasonal distribution of ice which defines the location and development of the polynya; ice movement, which is indicative of the relative importance of latent and sensible heat processes; ice concentration at different scales in the area centered on the sampling station, which determines the underwater light regime experienced by organisms and the rate of local warming of the surface layer. In the short-term, variations in ice cover and ice thickness modify the amount of light available to ice algae, phytoplankton and visual predators such as fish larvae. In the longer term, it affects the temperature experienced by algae, protozoans (unicellular) and metazoans (multicellular) organisms in the surface layer. Fine resolution satellite data are needed to identify the spatial scales at which biological processes, such as photosynthesis or larval fish feeding, are most sensitive to ice cover characteristics.

The distribution and movement of sea ice within the North Water will be studied using a combination of surface based and spaceborne satellite observations. In particular, the newly launched RADARSAT satellite will provide extremely precise maps of ice distribution and type. The objectives are to understand how the ocean and atmosphere control the thickness and distribution of sea ice throughout an annual cycle and to develop models through which we can make predictions about the response of the polynya to future environmental changes.

To contribute to the understanding of oceanographic and meteorological processes responsible for the generation and maintenance of the North Water, direct/indirect measurements of heat, momentum and salt fluxes as well as nutrient transport will be made through the snow and sea ice cover/at the ice-water interface/ under sea ice at different sites in the polynya. The proposed program is closely linked to the ice cover dynamics project. 

Numerical simulation using computers is a powerful tool by which direct observations and measurements of an oceanographic process can be expanded into a highly synthetic picture. The wealth of oceanographic, meteorological and ice data that will be collected during field work on the icebreaker, by the moored instruments and by satellites will be fed into numerical models that try and reproduce the observed seasonal pattern of opening and closing of the North Water.

Earlier modeling efforts suggest that both latent and sensible heat mechanisms may contribute to the opening and maintenance of the North Water. A wind-driven (latent-heat) model coupled with an upwelling (sensible-heat) model has been used to simulate the ice edge configuration and upper-ocean circulation associated with the North Water. The model suggests that the North Water is basically a latent-heat polynya early in the year and that sensible heat effects become important in late spring, close to the Greenland coast. This study will develop a time-dependent model of the North Water polynya, and use it to examine the generation, evolution, maintenance of the polynya and its response to weather patterns and low-frequency synoptic forcing. The field operations carried out within the NOW program will provide the measurements of the ocean circulation, temperature-salinity fields and mixed-layer depths in the North Water, especially off the west coast of Greenland, that are needed to determine the actual sensible heat flux. The synoptic picture of the ice velocity field both within and outside the polynya that will be obtained by remote sensing of ice cover will enable us to improve the ice dynamics in future models and supply the accurate ice concentration and thickness observations to determine ice edge characteristics.

Optics, nutrients, primary and export production ( Price, leader )
Booth, Cochran, Demers, Fukuchi, Gosselin, Larouche, Legendre, Price, Roy, Sasaki, Taguchi, Wallace, Watanabe.

According to our central hypothesis, the physical mechanism responsible for the generation of the polynya at a given time or in a given area will determine the timing of the local phytoplankton bloom. In the sensible heat case, the melting of the ice cover results in the immediate haline stratification of the surface layer which triggers the phytoplankton bloom. In the latent heat case, removal of ice by wind also favors the vertical mixing of the water column. Phytoplankton cells entrained at depth by vertical mixing receive too little light on average to grow. The phytoplankton bloom will be delayed until this vertical mixing is impeded by the summer warming of the surface layer. Hence, locally, the relative contribution of sensible-heat (melt) and latent-heat (wind) processes to the opening of the North Water will determine algal characteristics that include the timing of blooms, the size structure of primary production, the taxonomic composition of phytoplankton assemblages and the type of material dominating the particulate sinking flux. These will, in turn, influence the structure and productivity of the entire polynya ecosystem. In this project, we will relate the intensity of primary production and the nature of phytoplankton and ice algal assemblages to the different hydrodynamics regimes prevailing at different times and in the North Water and under the surrounding ice cover.

Recent discoveries indicate that bacteria may play a more important role than previously thought in the flux of carbon through marine ecosystems. Marine bacteria feed mainly on phytoplankton exudates and are preyed upon by microheterotrophs. They are also parasitized and destroyed by viruses. It has been proposed that the development of bacteria is impeded by the very cold temperatures prevailing in Arctic waters. Yet, the effect of cold on bacterial growth can be compensated by a greater availability of phytoplankton substrate. We propose that, in the sensible-heat parts (or periods) of the North Water, the early availability of phytoplankton and warmer temperatures will permit the full development of bacterial populations which will then be checked by microheterotroph predators and viruses. The development of this microbial food web would be slower in latent-heat parts of the polynya and under the ice cover where bacterial populations would be limited by low availability of phytoplankton and low temperature.

Changes in the activity of bacterioplankton or ingestion rates of protistan and metazoan grazers influence the CO₂ exchange between atmosphere and ocean, the carbon flow between dissolved pools and metazoan food webs as well as the magnitude and composition of sinking fluxes. This project will examine how the physical factors that stabilize the upper water column, and establish and maintain a gradient in temperature and phytoplankton abundance in the North Water influence (1) the activity of microbes, (2) prey selection and ingestion rates of protistan and metazoan grazers, and (3) the degree of coupling between microbes and metazoans. The intensity of this coupling will influence the nature and magnitude of the export of carbon to higher trophic levels and the deep-sea.

In previous sections, we hypothesized that the mechanism of generation of the polynya determine the timing of the phytoplankton bloom. The timing of the bloom, in turn, determines the length of the biological production season, i.e. the interval between the bloom and the freeze-up of the polynya in the autumn. This interval could be as long as 6 months in the sensible heat case, ca. 4 months in the latent heat case and < 2 months in non-polynya areas. In addition, the surface layer is expected to warm up earlier in the sensible heat case. Food availability and temperature are important factors in the regulation of animal fecundity, growth and development. Hence, how and when the polynya opens is predicted to affect the life cycles of planktonic herbivores and their predators, the local transfer of primary production towards the pelagic food web and the faecal component of the vertical particle flux. In the relatively simple food web of the Arctic marine ecosystem, the transfer of algal production to fish, birds and mammals is effected primarily through three metazoan groups: copepods, macrozooplankton predators and Arctic cod. We hypothesize that above-zero temperatures and a longer season of phytoplankton production will result in a longer and more intense production of copepods and macrozooplankton, and faster growth of Arctic cod larvae in sensible-heat areas of the North Water than in latent-heat areas or adjacent ice-covered waters. An extended season of production of copepods and the improved survival of Arctic cod larvae would explain the extraordinary abundance of planktivorous birds and piscivorous seals and whales in the North Water.

Arctic birds generally feed on plankton and juvenile fish (e.g. Arctic cod) which feed on the plankton. Whales and seals prey primarily on Arctic cod. Arctic seabirds and marine mammals are more abundant in and near polynya areas than in adjacent non-polynya areas. There are also large differences in the biomass of birds and mammals between polynyas. For example, the North Water is thought to support one of the highest biomasses of birds and mammals, whereas the Northeast Water Polynya on the eastern coast of Greenland is quite unproductive. It is generally believed that the concentration of mammals and birds in the North Water is a consequence of increased biological productivity which results in the greater availability of suitable plankton and fish prey. We also hypothesize that sensible and latent heat sources cause the algal bloom and food webs to develop differently on the east and west sides of the North Water which in turn determines the distribution and abundance of seabirds and marine mammals. In this project, we propose to test the above hypothesis by using stable isotope ratios, bioaccumulation of contaminants, direct sampling of birds and ringed seals to determine food habits, and land-based, aerial and shipborne surveys to quantify the distribution and abundance of seabirds and ringed seals. 

There is evidence that an ozone "hole" similar to that over the Antarctic is now developing over the Arctic. The increased UV radiation resulting from the depletion of the ozone layer threatens the biological productivity of all planktonic organisms living in the surface layer of the ocean. In the Arctic, populations in the open waters of polynyas are at greater risk than those under the protection of an ice cover outside the polynya. This project will assess the impact of present and predicted levels of UV radiation on the survival and productivity of algae, microheterotrophs, copepods and fish larvae in the North Water. We hypothesize that the impact of UVB radiation will be modulated by the physical processes leading to the formation of the North Water: when latent heat processes dominate, mixing will diminish exposure to harmful UV-B radiation in surface waters; conversely, when sensible heat processes dominate, stratification will increase this exposure, with potential negative effects on biological production, especially during spring-time.

A central goal of NOW is to quantify and compare the flows of carbon and energy through the pelagic food web, for different hydrodynamic conditions (i.e. ice-covered areas and gradient between sensible heat and latent heat situations) and periods in the season. This is crucial for assessing the significance of hydrodynamic conditions for the export of biogenic carbon towards higher trophic levels and into deep waters where some can be sequestered. The usual approach to obtain a complete picture of the carbon (or energy) flows in ecosystems is to build a flow diagram model, using the available estimates of production and consumption for as many components as possible of the food web. A more efficient approach will be used for the North Water. It consists in feeding available estimates and their standard errors into an inverse model, to calculate the most likely patterns of carbon flow. 

Carbon Cycling: Ecosystem Approach ( Legendre, leader )
Anderson, Bjornsen, Booth, Deibel, Demers, Falk, Fortier, Fukuchi, Gosselin, Hattori, Hobson, Hunt, Larouche, Legendre, Price, Rivkin, Roy, Runge, Sasaki, Satoh, Taguchi, Wallace, Watanabe, Welch.

The recent increase in atmospheric carbon dioxide due to the combustion of fossil fuels is a major cause of the greenhouse effect and global warming. By absorbing part of the excess CO₂ produced by humans (about 50 %), the oceans play a major role in retarding the greenhouse effect. The contribution of Arctic waters to this entrapment of CO2 is poorly known and this is a serious handicap for the development of more precise models of global climate change. A recent hypothesis suggests that the interaction between the seasonal cycles of microalgal production and ice formation make seasonally ice-covered seas particularly efficient at trapping atmospheric CO2. We propose to test key elements of this new theory. Using measurements of trophic fluxes for the major components of the food web, we will assess the export of biogenic carbon in the different hydrographic regimes prevailing in the North Water and under adjacent ice-covered areas.

Direct, quantitative, measurements of carbon export processes and pathways will be used to complement the carbon flux estimates based on food web dynamics (previous project). Assessment of organic carbon export from the euphotic zone will include examination of vertical transport as sinking particles, remineralization of dissolved organic carbon (DOC) to dissolved inorganic carbon (DIC) by biological and photochemical oxidation, transfer to higher trophic levels within the water column and in benthic ecosystems, and burial in the sediments. Indirect estimates of export will also be made from carbon inventories and tracer studies related to advective transport data and models generated as part of NOW. These measurements will result in clear constraints for estimation of the carbon dynamics (recycling vs. export) within the North Water, and the effects of changing ice cover on these fluxes. 

Microbial Particle Hydrolysis Below the Euphotic Zone ( Deming, leader )
Deming, Walsh, Rivkin

The magnitude and fate of particulate organic material that sinks from productive surface waters are essential elements in ecosystem models that aim to track carbon from atmospheric CO2 to burial in the sedimentary record. Polar regions of open water are uniquely characterized by strong seasonal fluctuations in organic fluxes and the North Water provides a remarkable opportunity to examine contemporary variations in flux within the productive season due to co-occurrence of both latent-heat and sensible-heat regimes and ecosystems. Tests of the hypothesis that low temperature may account for reduced hydrolysis rates of pelagic particles and a de-coupling of benthic hydrolysis processes from microbial metabolism will help explain the more efficient delivery of organic material to the seafloor and apparently greater role for higher benthic trophic levels than has been observed elsewhere in the Arctic. In the North Water, where the quality and quantity of vertical carbon fluxes are expected to vary with the physics of open-water formation, a significant opportunity exists for recognizing independent and combined effects of temperature and substrate availability on rates of particle hydrolysis. By examining particle hydrolysis along with bacterial respiration, we should be able to better define bacterial survival strategies at low temperatures and the importance of bacteria to trophic structure and carbon cycling in benthic environments underlying and downstream of the polynya. The geographic- and flux-specific rates we expect to generate will help to constrain models and measurements of particle fluxes and fates in this Arctic setting. 

Microalgae produce dimethylsulfide (DMS), a gas that plays a key role in the global sulfur cycle and also influences cloud formation and, therefore, local and global heat balances. Understanding how algae affect cloud formation in remote oceans may prove crucial for predicting Earth's response to global warming. In polar regions, both phytoplankton and ice algae may contribute to DMS production. The release of DMS to the atmosphere should occur primarily in the open waters, as the ice cover will reduce gas exchanges. Furthermore, increased biological activity (e.g. algal production and zooplankton grazing) in the open waters of the polynya should magnify the role of the North Water as a source of atmospheric DMS and clouds in the area.

We hypothesize that the relative importance of latent heat and sensible heat in the opening of the North Water will influence the spatio-temporal distribution of biogenic sulfur compounds in its sea water and cause local differences in the sea to air flux of dimethylsulfide (DMS). The sulfur compounds under consideration here are dimethylsulfoniopropionate (DMSP), dimethylsulfoxide (DMSO) and dimethylsulfide (DMS), a gas that may influence global climate. When and where latent heat mechanisms dominate, hydrodynamic and biological activity will result in low concentrations of dissolved biogenic sulfur compounds. The sea to air flux of DMS would be limited. In contrast, the sensible heat mechanism favours an early bloom of phytoplankton and the full development of bacterial populations. Nevertheless, the flux of DMS to the atmosphere would depend upon the export pathway. High zooplankton activity in surface waters would lead to elevated DMS concentrations in these waters and facilitate exchange across the air-sea interface. Alternatively, sinking of cells into deeper waters would limit the DMS flux to the atmosphere.